For patients with suspected Wilms tumors, preoperative staging studies should include a computed tomography (CT) scan of the abdomen/pelvis and chest. Preoperative assessment of intravascular extension of Wilms tumor is essential to guide management. The presence of intravenous tumor thrombus, which has been reported in up to 11.3% of Wilms tumor cases, can lead to differences in management. In North America, local staging of Wilms tumor is performed with CT or magnetic resonance imaging of the abdomen and pelvis. Contrast-enhanced CT has high sensitivity and specificity for detection of cavoatrial tumor thrombus in Wilms tumor cases that may impact surgical approach. Routine Doppler evaluation after CT has been performed is not required.
The stage is determined by the results of the imaging studies and both the surgical and pathologic findings at nephrectomy and is the same for tumors with favorable or anaplastic histology. Thus, patients should be characterized by a statement of both criteria (for example, stage II, favorable histology or stage II, anaplastic histology).[2,3]
The staging system was originally developed by the National Wilms Tumor Study Group and still used by the Children's Oncology group. The staging system and incidence by stage are outlined below.Stage I
In stage I Wilms tumor (43% of patients), all of the following criteria must be met:
- Tumor is limited to the kidney and is completely resected.
- The renal capsule is intact.
- The tumor is not ruptured or biopsied prior to removal.
- No involvement of renal sinus vessels.
- No evidence of the tumor at or beyond the margins of resection.
[Note: For a tumor to qualify for certain therapeutic protocols as stage I, regional lymph nodes must be examined microscopically.]Stage II
In stage II Wilms tumor (20% of patients), the tumor is completely resected, and there is no evidence of tumor at or beyond the margins of resection. The tumor extends beyond the kidney as evidenced by any one of the following criteria:
- There is regional extension of the tumor (i.e., penetration of the renal sinus capsule, or extensive invasion of the soft tissue of the renal sinus, as discussed below).
- Blood vessels within the nephrectomy specimen outside the renal parenchyma, including those of the renal sinus, contain tumor.
[Note: Rupture or spillage confined to the flank, including biopsy of the tumor, is no longer included in stage II and is now included in stage III.]Stage III
In stage III Wilms tumor (21% of patients), there is residual nonhematogenous tumor present following surgery that is confined to the abdomen. Any one of the following may occur:
- Lymph nodes within the abdomen or pelvis are involved by tumor. (Lymph node involvement in the thorax or other extra-abdominal sites is a criterion for stage IV.)
- The tumor has penetrated through the peritoneal surface.
- Tumor implants are found on the peritoneal surface.
- Gross or microscopic tumor remains postoperatively (e.g., tumor cells are found at the margin of surgical resection on microscopic examination).
- The tumor is not completely resectable because of local infiltration into vital structures.
- Tumor spillage occurs either before or during surgery.
- The tumor is treated with preoperative chemotherapy and was biopsied (using Tru-cut biopsy, open biopsy, or fine-needle aspiration) before removal.
- The tumor is removed in more than one piece (e.g., tumor cells are found in a separately excised adrenal gland; a tumor thrombus within the renal vein is removed separately from the nephrectomy specimen). Extension of the primary tumor within vena cava into thoracic vena cava and heart is considered stage III, rather than stage IV, even though outside the abdomen.
In stage IV Wilms tumor (11% of patients), hematogenous metastases (lung, liver, bone, brain), or lymph node metastases outside the abdominopelvic region are present. The presence of tumor within the adrenal gland is not interpreted as metastasis and staging depends on all other staging parameters present. The primary tumor should be assigned a local stage following the above criteria which determines local therapy. For example, a patient may have stage IV, local stage III disease.Stage V and those predisposed to developing Wilms tumor
In stage V Wilms tumor (5% of patients), bilateral involvement by tumor is present at diagnosis. Previously an attempt was made to stage each side according to the above criteria on the basis of the extent of disease. The current COG-AREN0534 protocol recommends preoperative chemotherapy in hopes of reducing tumor size to allow renal-sparing surgical procedures. In these patients, renal failure rates approach 15% at 15 years posttreatment, making renal-sparing treatment important.References
- Khanna G, Rosen N, Anderson JR, et al.: Evaluation of diagnostic performance of CT for detection of tumor thrombus in children with Wilms tumor: a report from the Children's Oncology Group. Pediatr Blood Cancer 58 (4): 551-5, 2012. [PUBMED Abstract]
- Wilms' tumor: status report, 1990. By the National Wilms' Tumor Study Committee. J Clin Oncol 9 (5): 877-87, 1991. [PUBMED Abstract]
- Perlman EJ: Pediatric renal tumors: practical updates for the pathologist. Pediatr Dev Pathol 8 (3): 320-38, 2005 May-Jun. [PUBMED Abstract]
- Breslow NE, Collins AJ, Ritchey ML, et al.: End stage renal disease in patients with Wilms tumor: results from the National Wilms Tumor Study Group and the United States Renal Data System. J Urol 174 (5): 1972-5, 2005. [PUBMED Abstract]